The present invention relates to a cyclone separator for separating a multiphase fluid into its different fractions. In particular, the invention relates to a cyclone separator which is effective for separating a multiphase fluid comprising heavy, medium and light fractions into a heavy fraction and a mixture of light and medium fractions. In this manner, comparatively high heavy fraction/light fraction separation efficiencies may be achieved even when the fluid contains relatively large volumes of the light fraction.
Bulk de-oilers and hydrocyclones, which may be referred to generically as cyclone separators, are used in the hydrocarbon production industry to separate multiphase fluid streams into their different fractions so that these fractions may be treated separately. For example, cyclone separators are commonly used to separate the production fluid from a hydrocarbon well into separate streams of oil and water so that the oil can be conveyed to a processing facility and the water can be, e.g., re-injected into the well.
Prior art cyclone separators operate by rotating the production fluid to created centrifugal forces which cause the higher density water to move toward the outer portion of the fluid stream and the lighter density oil to move toward the middle of the fluid stream. The water is then discharged through a heavy fraction outlet and the oil is discharged through a separate light fraction outlet.
Although these prior art cyclone separators work relatively well when the production fluid contains relatively small amounts of gas, problems arise when the volume of gas in the production fluid is relatively large. This is due to the fact that the gas, being less dense than oil, is displaced toward the middle of the rotating production stream and consequently interferes with the discharge of the oil through the light fraction outlet. As a result, larger amounts of oils than desired are discharged through the heavy fraction outlet with the water.